Process for producing a glass body

ABSTRACT

Preforms for drawing into glass fibers are relatively quickly produced by extruding filaments or tapes from polysiloxanes and/or heteropolysiloxanes and curing such filaments. A cylindrical wound body is produced from such cured filaments by winding such filaments onto an arbor. The wound body is converted, by heating in an oxidizing atmosphere, into an oxide body composed of SiO 2  and, under certain conditions, containing doping amounts of select heteroelements present in the heteropolysiloxane. After removal of the arbor, a gas stream containing chlorine gas is flushed at a temperature of about 1000° to 12,000° C. through the oxide body to remove any traces of water and the dry oxide body is sintered into glass at a temperature of about 1200°-1500° C. The tubular preform thereby attained is collapsed and a glass fiber is drawn therefrom. This process is particularly suitable for the fabrication of gradient optical fibers. A desired refractive index profile can already be taken into consideration in the production of the wound body.

This is a division of application Ser. No. 536,954 filed Sept. 28, 1983which applicant issued as U.S. Pat. No. 4,547,210 on Oct. 15, 1985.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a process for producing a glass body andsomewhat more particularly to a method of producing a preform fordrawing into a glass light waveguide.

2. Prior Art

A process for optical fiber fabrication wherein silicon-organicmaterials are chemically converted into glass is known, for example fromElectronic Letters, Vol. 18, (1982) pages 499-500. This process adapts aglass production process known as the so-called "sol-gel process" foroptical fiber fabrication.

In other known optical fiber fabrication processes (see, for example,Chem. Engineering Technology, Vol. 51, (1979) pages 612-627) preformsfor drawing into glass fiber light waveguides are produced by depositingglass from a gaseous phase. High-grade fibers are produced by thistechnique, however, the production rate is quite low. The rate at whicha fiber preform can be produced by depositing glass from a gaseous phaselimits the production rate. Maximum rates of about 5 km/h, expressed inequivalent fiber length, have been attained.

Processes of the type initially referred to, which bypass the gaseousphase are suitable for higher production rates. With known processes ofthis type, one begins from a silicon alkoxide, i.e., from asilicon-organic material, which is hydrolyzed in its liquid phase and isjelled into a large volume body by means of polycondensation of silicicacid. A glass body can be produced from the resultant gel by means ofdrying and sintering. Preforms having desired gradient profiles,however, are difficult to produce with this technique.

SUMMARY OF THE INVENTION

The invention provides an improved process of the type initiallydiscussed for rapidly producing glass bodies and with which bodiespredetermined refractive indices or gradient profiles can be readilyattained.

In accordance with the principles of the invention, a body of a solidsilicon-organic material is chemically converted into a desired glassbody.

Thus, by following the principles of the invention, one no longerproceeds from a liquid but rather from a solid silicon-organic materialand attains glass bodies much more rapidly.

In preferred embodiments of the invention, the solid silicon-organicmaterials are selected from the class consisting of polysiloxanes,heteropolysiloxanes and mixtures thereof.

The refractive index of a glass body produced in accordance with theprinciples of the invention can be regulated by the nature of theheteropolysiloxanes utilized. With these solid silicon-organicmaterials, certain atoms therein can be partially substituted byheteroelements which determine the refractive index. In preferredembodiments, heteropolysiloxanes having at least some Si or O atomstherein, have at least some of their Si or O atoms substituted by atleast one heteroelement selected from the group consisting of B, Al, Ga,Ge, Sn, Pb, P, Sb, As, F, Ti, Zr, Nb, Ta, Sc, Y and mixtures thereof andare utilized to attain a desired refractive index.

A particular advantage of polysiloxanes and heteropolysiloxanes, whichare also known as silicone caoutchouces, is that these materials can beproduced free of foreign metal contaminations from distillable monomers,such as alkyl chlorosilanes.

In certain embodiments of the invention, the solid silicon-organicmaterials can include a finely dispersed compatible oxide fillermaterial or can be "filled" with such materials. Further, thesilicon-organic materials can be admixed with certain compatiblehardeners as an aid in producing filaments or tapes from such materials.

In the practice of the principles of the invention, during conversion ofa solid silicon-organic material into glass, the body of such materialcan be heated in an oxidizing atmosphere whereby the C--H components ofthe silicon-organic material are oxidized and removed while SiO₂ and,under certain conditions, oxides of any heteroelements present remainand the oxide body so-attained is sintered into glass.

In certain preferred embodiments of the invention, the above oxidizingatmosphere can be pure oxygen or an oxygen-helium admixture. In certainpreferred embodiments, the attained oxide body is sintered into glass ata temperature of about 1200° to 1500° C.

In certain embodiments of the invention, in order to eliminate traces ofwater that may be present, the oxide body, which is porous, is flushedwith a stream of chlorine gas or chlorine gas in a helium carrierstream, at a temperature of about 1000° to 1200° C. before sintering. Atthese temperatures, hydrogen chloride is formed and can be carried outof the reaction chamber in the moving gas stream.

In certain embodiments of the invention, particularly for production ofglass bodies having a predetermined refractive index profile, a woundbody of filament-shaped or tape-shaped silicon-organic material isutilized as the starting body.

Predetermined refractive index profiles can be attained by forming awound body from different filaments and/or tapes. These filaments ortapes can differ both in terms of their composition as well as in termsof their dimension or cross-sectional shapes.

In certain embodiments of the invention, a wound body which exhibitsdifferent compositions ply-wise, comprised of different filaments and/ortapes, can be utilized for producing a glass body and is particularlysuitable for production of rod-shaped preforms having a radialrefractive index profile useful for producing gradient fibers. With thistype of wound body, the composition of different filaments and/or tapescan change from ply to ply while the composition can remain constantwithin one ply. With a cylindrically wound body, this means that thecomposition of different filaments or tapes changes only in a radialdirection while it remains constant in the longitudinal direction. Thisproperty is fully retained upon chemical conversion of such a body intoglass.

In certain embodiments of the invention, extruded polysiloxane and/orextruded heteropolysiloxane filaments and/or tapes are wound onto acylindrical arbor. In certain preferred embodiments, the arbor comprisesa ceramic rod, preferably composed of Al₂ O₃, which can be provided witha relatively thin coating of an organic polymer release agent.

In certain embodiments of the invention, a polysiloxane filament or tapeand a heteropolysiloxane filament or tape are simultaneously wound ontoan arbor and/or a filament or tape composed of apolysiloxane/heteropolysiloxane mixture of constant or variablecomposition is wound onto an arbor and/or a composite filament or tapehaving a core and a jacket is wound onto an arbor, with the core beingcomposed, for example, of a heteropolysiloxane or a polysiloxane and thejacket being composed of, for example, a polysiloxane or, respectively,a heteropolysiloxane.

In certain embodiments of the invention as set forth above, a wound bodyof filaments or tapes of silicon-organic material is formed by beginningthe winding with a high component of heteropolysiloxane filaments,threads or tapes and then gradually reducing this component as thewinding proceeds.

Likewise, in certain embodiments of the invention as set forth above, apolysiloxane filament or tape of a select diameter and a relativelythicker heteropolysiloxane filament or tape are wound simultaneouslyinto a body and the relatively higher heteropolysiloxane componentso-attained in an initially wound body is reduced by a cross-sectionalchange whereupon, under certain conditions, only polysiloxane filamentsor tapes are then applied.

In certain embodiments of the invention, filaments, threads or tapesutilized in forming a select body composed of a silicon-organicmaterial, are produced by extruding such material and curing the same bya subsequent thermal treatment, preferably at a temperature of about500° C. Further, compatible hardening agents can be initially added tothe silicon-organic materials and function, on the one hand, as a meansfor shape retention of the extruded filaments or tapes and, on the otherhand, as a means of preventing vaporization of the siloxanes duringsubsequent steps involving thermal treatment. Additionally, filaments ortapes can be composed of a polysiloxane/heteropolysiloxane mixturehaving a composition which is set or varied by an appropriate mixingmeans connected to the input end of an extruder.

In certain embodiments, the winding arbor utilized to organize thefilaments or tapes of the silicon-organic material into a desired body,is removed from such body after the chemical conversion (oxidation) ofthe filaments or tapes making-up the body. The resultant oxide body canbe readily removed from the arbor after incineration of a releasingagent, which may be present on the winding arbor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further explained in somewhat greater detailbelow, referring to an exemplary embodiment and the flow diagramillustrated in the FIGURE.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the flow diagram, a select polysiloxane and a selectheteropolysiloxane are utilized as the base or initial startingmaterials. These starting materials can be premixed with one or morefinally dispersed oxide fillers, a compatible hardener and/or with oneanother in a desired ratio and then fed to the input end of an extrusionmeans.

In the embodiment illustrated, a base polysiloxane material is fed to anextruder and polysiloxane filaments or the like of a desiredcross-sectional shape and dimension are extruded from the basepolysiloxane material. These extruded polysiloxane filaments or tapesare cured by means of a brief, thermal post-cross-linking reaction at atemperature of about 500° C.

Simultaneously, a base heteropolysiloxane material (with or without oneor more heteroelement atoms therein) is fed into an extruder andheteropolysiloxane filaments or the like of a desired shape and diameterare extruded from the base heteropolysiloxane material and are cured bymeans of a brief, thermal post-cross-linking reaction at a temperatureof about 500° C.

As earlier mentioned, the curing step, with the use of a previouslyadded hardener, functions on the one hand, for shaped retention of theformed filaments, tapes or threads and, on the other hand, forpreventing undue vaporization of the siloxanes during subsequent stepsinvolving thermal treatment.

The cured siloxane polymer filaments or tape are then wound onto acylindrical arbor. The arbor comprises a ceramic rod, which has beencomposed, for example, of Al₂ O₃ and has been provided with a relativelythin coating of a compatible organic polymer functioning as a releaseagent.

The wound body generated by winding the filaments onto the arbor isgenerally cylindrical in shape. A predetermined radial refractive indexprofile determines the compositions of the filaments to be wound intothe body. When, for example, a core-jacket fiber, i.e., a fiber having astepped refractive index profile, is to be produced, then one canproceed in such a manner that, first, a polysiloxane filament and aheteropolysiloxane filament are simultaneously wound onto the arbor sothat a number of plies having this filament composition is produced.Next, only a polysiloxane filament is wound onto the earlier wound pliesso that an outer layer of a number of plies containing only polysiloxanearises. The core of the fiber is later generated from the inner plies ofthe polysiloxane and the heteropolysiloxane filaments and the jacket ofthe optical fiber is generated from the outer plies of polysiloxanes.

Instead of two filaments as set forth above, a single filament composedof a polysiloxane/heteropolysiloxane mixture can also be extruded, withthe composition thereof being set or continuously varied by a mixingunit connected to the input of an extruder. A composite filament havinga core and a jacket can also be utilized, consisting, for example, ofheteropolysiloxane in the core and polysiloxane in the jacket.

In the production of a gradient optical fiber, the filament compositecan be gradually altered ply-by-ply as required. For example, one couldbegin building or winding a body with a high component of a selectheteropolysiloxane filament, which during the course of time, isgradually allowed to decrease toward the outside of the body and, undercertain conditions, only polysiloxane filaments are then put in place sothat later these polysiloxane filaments form a jacket of the ultimatelyattained gradient fiber. The polysiloxane component of a body can, forexample, also be regulated by the cross-sections of a heteropolysiloxanefilament applied simultaneously with a polysiloxane filament. When thecross-section of the heteropolysiloxane filament is continuously changedduring winding, then the heteropolysiloxane component also changescontinuously. In a specific example, winding of a body began with aheteropolysiloxane filament which was thicker than the simultaneouslyapplied polysiloxane filament and the diameter of the heteropolysiloxanefilament was gradually allowed to decrease to zero, whereupon only thepolysiloxane filament was applied or wound to form an outer layer of thebody.

In order to convert the wound body into a glass body, the wound body isheated in an O₂ or an O₂ --He atmosphere at temperatures up to about1000° C. so that the C--H components of the siloxanes are removed by wayof oxidation. In this manner, an oxide body of SiO₂ is attained, which,under certain conditions, contains oxides of the heteroelementscontained in the initially applied heteropolysiloxanes. The high gaspermeability produced by the filament interstices of the wound body isadvantageous in further processing and guarantees a more uniform andfaster conversion to SiO₂ throughout the cross-section of the body. Atendency of the body to flake is thereby reduced and undesirable siliconcarbide formation is suppressed.

Heating of the wound body is preferably slowly executed at temperaturesof from about 0° . . . 1000° C. and most preferably at about 300°through 600° C. (in about 3 to 24 hours). In this manner, swelling ofthe siloxanes, due to a too fast development of reaction gases, can beavoided. Otherwise, a blistery and voluminous material having a lowconsistency could be obtained.

The winding arbor is expediently removed from the oxide body after thethermal-oxidation. Typically, the arbor is easily withdrawn from theoxide body after incineration of the releasing agent initially appliedonto the arbor.

In order to eliminate traces of water that may be present, the porousoxide body is then flushed with a heated gas stream comprised of eitherchlorine gas or a mixture of chlorine gas in helium. Hydrochloric acidis formed at temperatures of about 1000° to 1200° C. and is carried outof the reaction or drying chamber with the moving gas stream.

After drying, the oxide body is sintered into glass at a temperature ofabout 1200° to 1500° C. A transparent glass tube results which is nowcollapsed into a solid rod in a drawing furnace at a temperature ofabout 1900° C. and is substantially simultaneously drawn into a glassfiber.

An advantage of the inventive process described above is that adirected, highly focused material stream having a relatively highvelocity up to the cold preform can be readily realized.

The invention is further illustrated by reference to the followingexemplary aspects of the invention. Those skilled in the art willappreciate that other and further embodiments are obvious and within thespirit and scope of this invention, from the teachings of the presentexamples, taken in conjunction with the accompanying specification.

EXAMPLE 1 Preparation of the Polysiloxanes and the Heteropolysiloxanes

Methods for the preparation of polysiloxanes are widely known from theliterature (e.g., W. Noll, Chemie und Technologic der Silicone, VerlogChemi, Weinheim, 1968 and cited literature).

For example, a mixture of dimethyl-dichlorosilane,trimethyl-chlorosilane and methyl-trichlorosilane in a molar ratio ofabout 100:10:1 is prepared and hydrolyzed by the addition of water. Theresulting hydroxy silanes polymerize into silicone polymers. Forincreased cross-linkage, after extrusion of these branched chainmolecules, it is recommended to add vinyl groups (CH₂ ═CH--), e.g., inthe form of trivinyl-chlorosilane, to the mixture before hydrolization.Typical molar mixing ratios are 1:500 to 1:10,000, vinyl to methylgroup.

In the preparation of the heterosubstituted silicones, part of themethyl-chlorosilanes in the above described batch are substituted bytetrachloro germanium, GeCl₄, or by dimethyl-dichloro-germanium, (CH₃)₂GeCl₂, in a molar ratio of about 1:20 up to about 1:5 germanium tosilicon compounds. Of course, other heteroelements can be similarlyutilized to prepare a desired heteroelement polysiloxane.

EXAMPLE 2 Addition of Filling Materials

In order to achieve a high mass fraction of inorganic constituents inthe silicon-organic material utilized in producing glass bodies, up toabout 50% by weight of silica (SiO₂) and germania (GeO₂) are added tothe hydroxy silane bath in a finely dispersed form. Both of theseinorganic filler materials are obtained in small grained and highly pureform by flame hydrolysis of tetrachlorosilane and tetrachlorogermane.This occurs by injection of the vaporized compounds in an oxyhydrogenflame at temperatures between 700° to 1500° C., followed by an airquenching of the gas stream and filtering off the resultant particularmaterial from the cooled stream. Pyrogenic silicas of this type as wellas other heteroelement oxides are commercially available.

EXAMPLE 3 Extrusion and Filament Preparation

Before the extrusion of a viscous polymeric batch, about 0.6 to 1.2% byweight of organic peroxides, e.g., dibenzylperoxide orbis-(2,4-dichlorobenzoyl)-peroxide, are added by homogeneous dispersionas a cross-linking and thereby hardening agent. The extruded viscousfilaments are cured within a short furnace at a temperature betweenabout 300° and about 500° C., with a residence time ranging betweenabout 1 and 10 seconds to yield elastic rubber-like filaments. Thecross-section of these filaments ranges between about 1 and 10 mm². Withthis procedure, a filament with a constant germanium content can befabricated. Changing the composition of the silicone flow into theextruder by using two batch reservoirs, one containing theheteropolysiloxane, allows production of a filament having a variablegermanium content along the length thereof.

EXAMPLE 4 Winding of a Filament

An extruded filament is layerwise wound onto a rotating and axially toand fro shifting arbor. To obtain a preform for a step index fiber,first a germanium doped rubber-like silicone fiber is wound. This firstbody is the precursor material for the fiber core. Then a germanium-freefilament is wound onto this first body as the cladding material. Thetotal diameter of the composite body is typically about 10 cm. Thediameter ratio of the core and cladding region depends upon the targetfiber dimensions, e.g., 40% core regions for a multi-mode fiber and 6%core regions for a single-mode fiber having a 125 μm diameter.

To obtain a preform for a gradient-index fiber, one way is to windsimultaneously two filaments, one such filament being doped withgermanium. The cross-section of the latter is continuously and linearlyreduced with time until the core region is completed In this manner, aparabolic germanium concentration profile results, with a maximumconcentration in the central region.

A second way is to wind one filament with a continuously decreasinggermanium concentration. The molar mass flow rate of germania to silicaprecursors is adjusted in such a way that the total molar flow rate iskept constant and the germania flow rate is decreased linearly withtime, down to zero at the core cladding boundary. Thereby and by theeffect of a decreasing diameter growing rate of the cylindrical body, aparabolic germania profile is achieved, which results in a correspondingindex profile.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in thehereto-appended claims.

I claim as my invention:
 1. A process of producing a glass body preformfor use in drawing a glass light waveguide, said process comprising thesteps of producing filaments composed of a silicon-organic material withat least one filament being of a different composition from the otherfilament to provide different filaments of different compositions,winding said different filaments into a wound body of saidsilicon-organic material, and then chemically converting thesilicon-organic material into glass to convert the wound body into aglass body preform having at least two layers of a differentcomposition, said chemically converting including oxidizing thematerial, drying the oxidized material, and then sintering the oxidizedmaterial into the glass body.
 2. A process as defined in claim 1,wherein said solid silicon-organic material is at least onesilicon-organic compound selected from the class consisting ofpolysiloxanes, heteropolysiloxanes and mixtures thereof.
 3. A process asdefined in claim 2, wherein said heteropolysiloxanes have at least someSi or O atoms thereof substituted by at least one heteroelement selectedfrom the group consisting of B, Al, Ga, Ge, Sn, Pb, P, Sb, As, F, Ti,Zr, Nb, Ta, Sc, Y and mixtures thereof.
 4. A process as defined in claim1, wherein said solid silicon-organic material includes one or morefinally dispersed compatible oxide filler materials.
 5. A process asdefined in claim 1, wherein during said chemical conversion of saidsolid silicon-organic material into a glass body, said body is heated inan oxidizing atmosphere whereby the C--H components of saidsilicon-organic material are oxidized and removed while SiO₂ and oxidesof heteroelements remain, and the oxide body so-attained is sinteredinto glass.
 6. A process as defined in claim 5, wherein said body isheated in an oxygen atmosphere or an oxygen-helium atmosphere.
 7. Aprocess as defined in claim 5, wherein said heating occurs in a periodof 3 to 24 hours at temperatures ranging from about 300° through 600° C.8. A process as defined in claim 5, wherein said oxide body is sinteredinto glass at a temperature ranging from about 1200° through 1500° C. 9.A process as defined in claim 5, wherein, said drying comprising saidoxide body being flushed with a heated gas stream composed of chlorinegas or a mixture of chlorine gas in helium, said gas stream being heatedto a temperature in the range of about 1100° to 1200° C.
 10. A processas defined in claim 3, wherein said filaments composed of saidsilicon-organic material are wound onto an arbor for producing saidwound body.
 11. A process as defined in claim 10, wherein said arbor iscylindrically-shaped.
 12. A process as defined in claim 11, wherein saidarbor is a ceramic rod.
 13. A process as defined in claim 12, whereinsaid ceramic rod is composed of Al₂ O₃.
 14. A process as defined inclaim 10, wherein said arbor includes a relatively thin coating on itsouter surface composed of an organic polymer release agent.
 15. Aprocess as defined in claim 10, wherein a polysiloxane filament and aheteropolysiloxane filament are simultaneously wound onto said arbor toform the wound body.
 16. A process as defined in claim 10, wherein afilament composed of a polysiloxane/heteropolysiloxane mixture ofconstant or variable composition is wound onto said arbor to form thewound body.
 17. A process as defined in claim 10, wherein a compositefilament having a core and a jacket is wound onto said arbor to form thewound body, said core being composed of a heteropolysiloxane or apolysiloxane and said jacket being composed of a polysiloxane or,respectively, a heteropolysiloxane.
 18. A process according to claim 1,wherein the step of producing filaments includes extruding thesilicon-organic material into filaments and then curing the extrudedfilaments by a subsequent thermal treatment.
 19. A process as defined inclaim 18, wherein said filaments are cured by a thermal treatmentcomprising heating said filaments to a temperature in the range of about500° C.
 20. A process as defined in claim 18, wherein a compatiblehardening agent is admixed with said silicon-organic material prior toextrusion thereof into filaments.
 21. A process as defined in claim 18,wherein said cured filaments are wound onto an arbor to form said woundbody, said wound body being heated in an oxidizing atmosphere at atemperature in the range up to about 1000° C. so as to chemicallyconvert said silicon-organic material into an oxide material containingSiO₂, and removing said arbor after said conversion.
 22. A processaccording to claim 1, wherein the step of winding the differentfilaments wind the filaments as plies with one filament for each ply sothat the plies have different compositions.
 23. A process according toclaim 1, wherein the step of winding the different filament forms plieswith the composition of the filaments changing ply-to-ply and remainingconstant within a single ply.
 24. A process according to claim 1,wherein said step of winding produces a cylindrical wound body withplies and the composition of the filaments of each ply changes only in aradial direction of said body while remaining constant in a longitudinaldirection of said body.
 25. A process according to claim 16, whereinsaid step of producing filaments provides filaments of a classconsisting of polysiloxanes, heteropolysiloxanes and mixtures thereofand said step of winding starts with filaments having a relatively highcomponent of the heteropolysiloxanes and then uses filaments having areduced amount of the component.
 26. A process according to claim 25,wherein a polysiloxane filament of a given diameter and a relativelythicker heteropolysiloxane filament are wound simultaneously onto thearbor and the relatively high heteropolysiloxane component therebyproduced in the body being formed is reduced by a cross-sectional changeof said heteropolysiloxane filament, whereupon said polysiloxanefilament is wound to finish producing said wound body.
 27. A processaccording to claim 18, wherein said solid silicon-organic material isselected from the class consisting of polysiloxanes, heteropolysiloxanesand mixtures thereof and wherein the step of producing a filamentextrudes a filament composed of a polysiloxane/heteropolysiloxanemixture from an extrusion means and then cures the filament, thecomposition of said filament being set or varied by a mixing unitconnected to an input end of said extrusion means.